Throttle control: Notes

1. Pedal arm with mounting for accelerator cable (rotates pedal position sensors).
2. Return spring on pedal arm (not visible, located behind the pedal arm).
3. Pedal position sensors (2 potentiometers)
4. Motor (brushless DC motor, rotates throttle spindle and disc, throttle position sensor and throttle arm).
5. Throttle
6. Throttle arm
7. Return spring for throttle arm
8. Throttle position sensors (2 potentiometers)
9. Limp-home solenoid (activated 5 times in succession on limp-home and each time the ignition is turned on if a diagnostic trouble code that puts the throttle into limp-home mode is stored in the control module memory. If the throttle is put into limp-home mode, the toothed disc will be disengaged).
10. Toothed disc (spring loaded by the throttle arm return spring and released by the limp-home solenoid when the throttle goes into limp-home mode. The disc must be reset manually after repair and deletion of the diagnostic trouble code).
11. Air after throttle (nipple for purging the EVAP canister).
12. Air after throttle (nipple for connecting crankcase ventilation).
13. Air before throttle (nipple for connecting to control valve for the turbocharger bypass valve).
14. (Not used).
15. Pre-heating (2 nipples for coolant circulation to reduce risk of ice forming).
16. 10-pin connector (2 for motor, 2 for 5V, 2 for ground, 2 for pedal sensor outputs and 2 for throttle position sensor outputs).

The throttle valve is turned by a brushless throttle motor supplied with a 600 Hz PWM signal from control module pins 24 and 48. The control module can turn the throttle valve in both directions by reversing the motor poles. The PWM ratio increases as the throttle valve moves further away from its nominal value.

Two throttle position sensors are connected to the throttle spindle. The sensors consist of potentiometers which are supplied with 5 V from control module pins 46 and 69, which are internally connected to each other in the throttle body, and grounded via control module pins 22 and 70 which are also connected to each other inside the throttle body.

The voltage from sensor 1 is connected to control module pin 33 and increases with the throttle position. The voltage from sensor 2 is connected to control module pin 10 and decreases with the throttle position. The sum of the two sensor voltages is therefore always about 5 V.

The voltage from sensor 1 is used by the control module as a value for the current throttle position.

The air mass control requests a certain air mass/combustion. The throttle control converts this value into a requested value for throttle position sensor 1 and compares this with the sensor's current value.

The difference gives rises to a throttle motor PWM signal with a polarity which turns the throttle valve until its current value corresponds to that requested.

If a major fault should occur in the throttle control, the control module will ground pin 36 and the limp -home solenoid will operate. The solenoid, which is located on the throttle body, then connects the pedal cable to the throttle spindle. The throttle motor is de-energized and the throttle is then controlled directly from the accelerator pedal.

The limp-home solenoid is first activated for 1 s and then for 4 x 0.5 s.

When the total air mass/combustion requested by the system has been calculated, it must be realized first by the throttle and then, if necessary, by the turbo control.

The requested air mass/combustion is corrected by the air density before the throttle. Thinner air requires a larger throttle angle to achieve the same air mass/combustion. The density of the air is calculated on the basis of the charge air pressure and the temperature of the intake air.

The value is then converted into a requested voltage for throttle position sensor 1. The throttle motor turns the throttle valve until the current sensor voltage corresponds to that requested.

The control module then checks that the current air mass/combustion corresponds to that requested. If necessary, fine adjustment of the throttle position is performed.

If a safety -related fault occurs in the throttle control system, the throttle will go into limp -home mode. The CHECK ENGINE lamp then comes on immediately and the diagnostic trouble code must be cleared with the diagnostic tool.